In-vitro study of the third occipital nerve near the C2-3 facet joint and the association between its morphology and the presence of a third occipital nerve notch.

Introduction: Occipital neuralgia, a debilitating condition characterized by headaches and neck pain, has been linked to the third occipital nerve (TON). Despite its potential role in this condition, the TON's relationship with surrounding structures, particularly the facet joint at the C2-3 level, remains poorly understood. Method: A comprehensive anatomical study was conducted on 35 embalmed and 5 fresh-frozen human body donors to investigate the relationship between the TON and the C2-3 facet joint. The TON was dissected, and its morphology described using a checklist. 3D coordinates of anatomical landmarks were registered using a Microscribe digitizer, nerve crossing angles and crossing locations were calculated. A logistic regression model was used to examine the association between the presence of a TON notch and degenerative/morphological characteristics. Results: A slight notch was observed in 33 % of the facet joints and a clear notch in 7.7 % of the facet joints. Higher levels of joint degeneration, more lateral crossings of the TON, and a small separation between the nerve and the facet joint were independently associated with a higher odds of a TON notch. Additionally, a correlation was observed between the location and the angle of the nerve crossing and with the presence of a notch. Conclusion: This study highlights the importance of degenerative and morphological factors in the occurrence of a TON notch in the C2-C3 facet joint. These results may have important clinical implications for diagnosis and treatment of occipital neuralgia and underscore the need for detailed anatomical assessments in patients with occipital headaches.